* @param parent the parent cell
* @throws org.jdesktop.wonderland.common.cell.MultipleParentException
*/
void setParent(CellMO parent) throws MultipleParentException {
if (parent!=null && parentRef!=null)
throw new MultipleParentException();
if (parent==null) {
this.parentRef = null;
this.parentCellID = CellID.getInvalidCellID();
} else {